Drive mechanism



I Sept. 30, 1958 E. N. SCOTT DRIVE MECHANISM Filed Sept. 21, 1955 50L [NO/D m/pur TERM/NAZS 0/50 T/OIVS OF M0 mw/vr OF I N V EN TOR. flew/v A! Scarf Mom? United States Patent DRIVE MECHANISM Ervin N. Scott, Moorestown, N. J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Air Force Application September 21, 1955, Serial No. 535,616

Claims. (Cl.,7487) The present invention relates to an improved reciprocating drive mechanism which is particularly applicable to the control of a scannable antenna.

It is an object of the present invention to provide an improved driving arrangement for cyclically driving a load through a selected one of two different angles of scan.

Another object of the invention is to provide an improved arrangement for selectively scanning different angles of scan having a common limit angle.

According to the invention, a load such as an antenna reflector is pivotally mounted on a support. A driving means such as an electric motor or the like. The mechanical coupling between the motor and the antenna reflector has a given extended length. The coupling includes a crank arm on the motor shaft and a linkage connected between the free end of the crank arm and a point on the antenna reflector displaced from its pivotal mounting to the support. Means are provided for changing the effective length of the crank arm while maintaining the extended length of the mechanical coupling the same.

This permits the antenna reflector to be scanned through angles of different size but having a common limit of rotation. This type of performance is especially useful in height-finder radars wherein the antenna must scan through a relatively small elevation angle when a target is at a long range and a relatively large elevation angle when the target is at a relatively short range, and where the lower extremity of scan must be the same for both modes of operation.

The invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a sketch of the arrangement of the present invention;

Figure 2 is a more detailed, perspective view of the arrangement of Fig. 1;

Figure 3 is a cross section through the coupling link of the arrangement of Fig. 2; and

Figure 4 is a cross section taken along line 4--4 of Fig. 3.

Referring to Fig. 1, antenna reflector 10 is pivotally mounted on pedestal 12 and is rotatable about axis .14. The driving means for the antenna is indicated schematically by box 16 and may comprise an electric motor or the like. The coupling between the motor and the an tenna reflector includes a crank arm or member 18 on the motor shaft, an end member 22 pivotally connected to the antenna, and a center link 20 connecting members 18 and 22. In one mode of operation, link 20 is locked to end member 22 and pivotally connected to crank member 18. The motor rotates member 18 about axis 26 and antenna reflector 10 scans through a relatively small angle of elevation. In its second mode of operation, center link 20 is locked end-to-end with crank member 18 and pivotally connected at axis 28 to end member 22. Now the driving means rotates the arm consisting of member 18 and 20 connected end-to-end about center of rotation 26 and the antenna reflector scans through a larger angle of elevation. The maximum depression angle, however, is common for both modes of operation since in both modes the" extended length of members 18 and 20, and link 22 is the same.

Fig. 2 shows the arrangement of Fig. 1 in greater detail. The shaft of motor 16 rotates member 18 with respect to axis 26. Solenoid 30 located in control link 20 is of the double acting type, with a mechanical lock at the stroke extremities. Power is supplied to the solenoid from a source 32 through brushes 34 and 34a and slip rings 36 and 36a. In one position of the solenoid, end member 22 is locked to link 20 end-to-end and the crank arm consists of the length of arm 18 between dashed lines 24 and 26. In the other position of the solenoid, arm 18 is locked end-to-end with link 20 and the length of the crank arm comprises the distance between dashed line 26 and 28.

Figs. 3 and 4 show in greater detail the locking arrangement. For the sake of drawing simplicity only cams 38 and 40 are shown in Fig. 3; however, Fig. 4 shows the complete locking arrangement including the solenoid 3t), and the link 31 driven by the toggles. Cams 38 and 40 are formed with grooves 42 and respectively in their circumferentialsurfaces ,(shown only in Fig. 4). When solenoid 30 is in its maximum retracted position, the one shown in Fig. 4, links 44 and 46 of the toggle have forced pawl 48 into the slot in cam 38. This locks control link 20 to end member 22 (see Fig. 2), and the antenna scans through a relatively small angle. At the same time that toggle 44--46 is moved, links 52 and 54 move pawl 56 out of the slot 50 in cam 40 so that axis 24 forms the pivot or the end of the crank arm of the reciprocating system.

When the solenoid shaft is in its maximum out position (left in Fig. 4) links 52 and 54 become aligned end to end, and pawl 56 is forced into slot 50 of cam 40. At the same time, the effective length of linkage 44, 46 is reduced, since point 58 is moved to the left, and pawl 48 is moved out of groove 42 in cam 38. This is the second mode of operation in which point 28 acts as the pivot or the end of the crank arm. Now the antenna scans through its maximum scan angle,

Following is a detailed description of what occurs when the solenoid is energized to move link 31 from its'most Y retracted to its outermost position (right to left in Fig.

4). As link 31 is forced to the left, it acts on link 70 through pin 74, pushing link 70 to the left. Link 70, in turn, acts on links 66 and 68 through pins 72 and 76, respectively, causing links 66 and 68 to move to the left. Pin 74 may be slightly off-centered with respect to link 70, as shown, in which case a greater force is exerted on link 68 than on link 66. Alternatively, pin 74 may be centered in link 70 so that the moment arms between pins 74, 72 and pins 74, 76 are of the same length, and the forces transmitted to links 66 and 68 are equal.

In operation, when the links of one toggle'are forced into end-to-end alignment, whereby further movement of the link (66 or 68) driving that toggle is prevented, link 70 is forced by the continued movement of link 31 slightly to rotate, and this rotation moves the second toggle into its fully retracted position. Note that the shoulders 62 and 64 on pawls 48 and 56, respectively, serve as stops to limit further rotation of the toggle links after they have been brought into end-to-end alignment.

Referring still to Fig. 4, as link 31 moves to the left, the links 5452 of the lower toggle are forced into endto-end alignment and the links 4446 of the upper toggle are forced out of end-to-end alignment. Further movement of link 31 to the left does not affect link 68 as that link now abuts a toggle which is in locked position (links 54, 52 in end-to-end alignment and link 52 abutting shoulder 64). Instead, this further movement of link 31 causes counter-clockwise rotation of link 70 about pin 74 (and pin 76); this, in turn, moves link 66 further to the left and completely retracts the links 44, 46 of the upper toggle. The retraction of links 44, 46, moves pin 60' downward and this pulls pawl 48 out of the slot 42 in cam 38. The reverse mode of operation is fundamentally the same and, therefore, need not be described here.

In a practical system designed for a long-range heightfinder radar, the maximum nod angle is approximately 25 for short range and the minimum nod angle is approximately 7/: for long range. The maximum depression angle of minus 2 is common to both angles. The angle changing device in control link 20 is remotely controlled from the operators position.

In a preferred form of the invention, the change from one mode of operation to another is done at the time when the antenna is at its minimum angle of scan, minus 2 in one form of the invention. It is at this time that the instantaneous torque forces are a minimum in the crank and link system. This is readily accomplished by proper indexing ofthe grooves in the cams.

As can be seen from Fig. 4, the design of the toggle mechanism precludes engagement of both pawls simultaneously when link 31 is at either of its extreme positions. Force multiplication in the toggle mechanism may be as high as 10 or more.

In the claims:

1. In an arrangement for producing reciprocating motion, in combination, supporting means, a load pivotable on said supporting means; driving means producing rotary motion; a mechanical coupling locked at one nd to said driving means and pivotally coupled at the other end to a point on said load displaced from the pivotal connection of the load to the supporting means, said mechanical coupling comprising three members, the center one of which is coupled at its ends to the other members; and means for locking the center one of themembers to either one of the end members in end-to-end aligned position, and pivotally coupling the remaining end member to the center member at the coupling between these two membets.

2. In an arrangement as set forth in claim 1, further including means for remotely controlling the last-named means.

3. In an arrangement as set forth in claim 1, said driving means comprising an electric motor.

4. In combination, a support, a load pivotally mounted on said support and including an extending arm; a rotatable drive shaft; crank arm means fixedly connected at one end to said drive shaft; link means pivotally connected at one end to the arm of said load; a control link connected at one end to the other end of said crank arm means and at the other end to the other end of said link means; and an arrangement for locking said control link in end-to-end alignment with either one of said means at the connection between said control link and said means, and pivotally connecting said control link to the other means at the connection thereof to said other means.

5. In the combination as set forth in claim 4, said 4 arrangement for locking including a solenoid, and means for remotely controlling said solenoid.

6. In the combination as set forth in claim 4, said arrangement for locking including a toggle mechanism for locking said control link to one of said means and unlocking said control link from the other of said means; and solenoid means for actuating said toggle mechanism.

7. In combination, a support; a load pivotally mounted on said support; a rotatable drive shaft; crank arm means fixedly connected at one end to said drive shaft; link means pivotally connected at one end to said load at a point on said load displaced from the latters point of mounting on said support; a control link connected at one end to the other end of said crank arm means and at the other end to the other end of said link means; and an arrangement for locking said control link with either one of said means in predetermined positional relationship, and pivotally connecting said control link to the other means at the connection thereof to said other means.

8. In combination, a support; a load pivotally mounted on said support; a rotatable drive shaft; a mechanical coupling of given extended length connected at one end to said drive shaft and pivotally coupled at the other end to a point on said load displaced from the pivotal mounting point of said load, said coupling including, as a portion of its extended length, a crank arm on said drive shaft; and means operatively associated with said mechanical coupling for changing the effective length of said crank arm while maintaining the extended length of said coupling the same.

9. In combination, a load adapted to be pivotally mounted on a support; a rotatable drive shaft; a mechanical coupling of given extended length connected between the drive shaft and a point on the load displaced from its pivotal mounting point, one portion of the extended length of said coupling comprising a crank arm on the drive shaft and the remainder of the mechanical couplingcomprising a linkage pivotally coupled at one end to the free end of the crank arm and at the other end to the load; and means operatively associated with said mechanical coupling for changing the ratio of the crank arm length to the linkage length while maintaining the overall length of the mechanical coupling the same.

10. In combination, a rotatable drive shaft; a mechanical coupling of given extended length connected at one end to the drive shaft and adapted to be connected at its other end to a pivotally mounted load, one portion of the extended length of said coupling comprising a crank arm on the drive shaft and the remainder of the mechanical coupling comprising a linkage pivotally coupled at one end to the free end of the crank arm and adapted to he pivotally coupled at its other end to the load; and means for adjusting the ratio of the length of the crank arm to the length of the linkage While maintaining the overall length of the mechanical coupling the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,399,493 Luehrs Apr. 30, 1946 2,717,518 Latta Sept. 13, 1955 

